// requires JQuery

sS hjs_humWithFade(double humVolume default 0.25) {

  ret hjs_playHum()

    + hjs(replaceDollarVars([[

      humSound.volume = 0;

      var humVolume = $humVolume; // level when on

      var humShouldBeOn = false;

      $.extend($.easing, {

        easeOutExpo: function(x, t, b, c, d) {

          return (t==d) ? b+c : c * (-Math.pow(2, -10 * t/d) + 1) + b;

        },

        easeInOutQuint: function (x, t, b, c, d) {

          if ((t/=d/2) < 1) return c/2*t*t*t*t*t + b;

          return c/2*((t-=2)*t*t*t*t + 2) + b;

        }

      });

      function humOn() {

        if (humShouldBeOn) return;

        humShouldBeOn = true;

        hum(humSound.volume); // start playing

        console.log("hum on (vol=" + humVolume + ")");

        fadeHumTo(humVolume);

      }

      // TODO: actually turn off in the end

      function humOff() {

        if (!humShouldBeOn) return;

        humShouldBeOn = false;

        console.log("hum off");

        fadeHumTo(0);

      }

      function fadeHumTo(vol) {

        $(humSound).animate({ volume: vol }, {

          duration: vol < humSound.volume ? 250 : 500,

          //easing: vol < humSound.volume ? 'easeOutExpo' : 'easeInOutQuint',

        });

      }

      function updateHumVolume(vol) {

        if (isNaN(vol) || humVolume == vol) return;

        humVolume = vol;

        console.log("New hum volume: " + vol);

        // fade to new value

        if (humShouldBeOn) {

          humShouldBeOn = false;

          humOn();

        }

      }

    ]], +humVolume);

}